1. Field of the Invention
This invention relates to a device for measuring critical dimensions of an object and, more particularly, for measuring thickness at a particular point, rate of taper and accuracy of the radius of the internal surface of a tapered, arcuate brake block. The brake block which is comprised of a friction material is fastened on its inside radial surface to a metal shoe and the assembled brake shoe is substantially installed in a drum brake mechanism in a well-known manner.
2. Summary of the Invention
One way to measure the distance between two surfaces or thickness of an object is to precisely locate one surface with respect to a fixed point and have a means for measuring the distance between the fixed point and the other surface. The thickness measurement is more complex when the solid object is tapered. This is because a first thickness measurement must occur at a given location on the object to establish a basic thickness, and a second measurement must take place at a second location a specified distance from the first location in order to obtain sufficient information to determine the rate of taper between the first and second locations. An example of a tapered object which is also curved is a brake block. The block has inside and outside surfaces formed on different radii. Since the internal surface of the brake block must be assembled on a shoe of matching radius, the accuracy of the internal surface radius must be measured as well as the thickness and rate of taper. Consequently, the subject device must accurately measure the thickness of a brake block at two points to determine rate of taper, and must also measure the variation of the internal surface radius from that specified for a matching shoe to which the block would be assembled.
The tapered block thickness gauge of the instant invention has a base plate which pivotally mounts a swing arm which has an indicator for visually indicating the variation of the radius of the internal surface of the brake block from the specified radius. A set pin is mounted on the base plate in order to zero the indicator at the specified radius. A pair of rest bars are mounted on the base plate and support the brake block at first and second measuring points. The rest bars are located from the axis of the swing arm a distance equal to the specified radius plus the specified thickness of the brake block at the respective measuring points. An end stop is attached to the base plate to retain the brake block in the proper position on the rest bars. The indicator is pivoted over the brake block to a first measuring point to check the brake block thickness with respect to that specified for that point. The indicator is then moved to the second measuring point to check the brake block thickness with respect to that specified for that point. As the indicator moves from the first measuring point to the second measuring point, the accuracy of the internal surface radius is indicated.
The subject gauge can be adapted to measure the accuracy of different brake blocks.